1. Field of the Invention
The invention relates to a device for comminuting bulk charge.
2. Description of the Background Art
When charge stock is comminuted in generic devices, a considerable part of the energy required for the comminuting is converted into heat. This is caused by friction and impact forces to which the charge stock is subjected during comminuting and which primarily act on the comminuting tools.
Known devices are characterized during operation by an air flow, which together with the centrifugal force is the cause of the transport of the charge stock inside the device. This so-called self-ventilation can be generated by the device itself and can optionally be additionally supported from outside with the aid of a blower. If the charge stock is not heat-sensitive, the innate self-generated flow of air in known devices is sufficient in order to cool down the comminuting tools so much that thermal damage to the charge stock is ruled out. Problems regularly occur when heat-sensitive charge stock is to be comminuted. In particular when plastics with a low softening temperature are to be comminuted, the operators of generic devices are faced with a difficult task. On the one hand, a milling of the charge stock is to take place just below the softening temperature in order to achieve the highest possible machine output. If the material-dependent limit temperature is thereby exceeded, the charge stock softens and begins to melt, with the result that individual particles agglomerate such that the size of the particles and the particle distribution of the comminuted material are no longer within the desired range. On the other hand, particles heated above the limit temperature are baked onto the machine parts and in particular the comminuting tools, so that the machine efficiency as well as the quality of the end product suffer as a result.
Foodstuffs and pharmaceuticals are cited as a further example of heat-sensitive charge stock, the chemical composition and effect of which are changed by an excessive heat generation, and losses in quality or even the uselessness thereof must thereby be accepted.
This problem is more marked in the case of fine milling, since it has been shown that the finer the end product to be produced, the more comminuting work has to be done, and the greater the heat generation in the region of the comminuting tools will be.
To avoid a thermal overloading of the charge stock during the comminuting thereof, it is known to lower the machine output of comminuting devices. In this way, less comminuting work is performed per unit of time, thus generating less excess heat. However, as a consequence, it must be accepted that the comminuting apparatus does not operate at full capacity, which goes against the fundamental requirement for an economical operation of such devices. There has therefore already been a change to increasing the quantity of cool air by means of additional blowers beyond the self-ventilation portion of a generic comminuting device, in order thus to be able to dissipate additional heat.
In connection with disk mills it is known to introduce additional cool air directly into the comminuting chamber to cool the milling tools. This takes place through openings in the housing front wall and/or housing rear wall, which are arranged around the rotational axis as close to the axis as possible. After its axial entry into the comminuting chamber through these openings, the cool air flows radially along the rear side of the rotor disk to cool the comminuting tools. A device of this type is disclosed, for example, in DE 10 2004 050 002 A1, which corresponds to U.S. Pat. No. 7,364,100, and which is incorporated herein by reference.
In U.S. Pat. No. 2,959,362 a cutting mill for producing plastic granules is described, which has a rotor equipped with blades over its circumference. The rotor is surrounded by a stator, in which the counter blades interacting with the rotor blades are arranged. A housing surrounds the stator at a clear distance, wherein cool air is blown into the space between the stator and the housing. After the absorption of thermal energy, the cool air is guided out of the housing via an outlet, in order to conduct the thermal energy produced during the cutting work out of the device.